The present invention generally relates to a compressor and more particularly, to a compressor of a movable slanting plate type to be used, for example, in a car air-conditioner for air-conditioning a motor vehicle or the like.
Recently, in the field of air-conditioning apparatuses for motor vehicles, there have been made various developments for achieving quick effects for cooling, heating, defrosting or the like, improvements on comfortable temperature and humidity control characteristics, reduction of burden on a motor vehicle engine, or reduction of fuel cost, etc. In compressors, as one means for such developments, performance control techniques therefor have been studied over a long period, some of which are now put into actual applications. One of such improvements relates to a wobble slanting plate type compressor disclosed, for example, in Japanese Patent Laid-Open Publication Tokkaisho No. 58-158382 in which, by arranging an inclination angle of a slanting plate to be variable through internal pressure control for a crankcase and utilization of a centrifugal force of a wobble plate, the stroke of a piston is altered to make a physical displacement or exhaust amount variable.
FIGS. 9 and 10 show a general construction of a conventional wobble slanting plate type compressor as referred to above.
In FIG. 9, the known compressor includes a cylinder block 1, a rear case 2 and a crankcase 3 tightly closing opposite end portions of said cylinder block 1, and a driving shaft 4 supported by radial roller bearings 5 and 6, and further held in an axial direction by thrust roller bearings 7 and 8 as shown. The cylinder block 1 has a plurality of cylinders 9 axially extending therethrough, and in each of the cylinders 9, a piston 10 is slidably mounted for reciprocating movement and connected for free directivity, a non-rotating wobble slanting plate 12 by a rod 11 through a ball joint portion 13. The wobble slanting plate 12 is mounted on a rotary driving plate 14 through a thrust roller bearing 15, and is axially retained by a thrust washer 16 and a retainer ring 17.
As is seen in FIG. 10, the rotary driving plate 14 is rotatably connected with a sleeve 18 slidably mounted on the driving shaft 4 by a pair of pivotal axis pins 19, with a common axis of said pins 19 intersecting at right angles with the axis of the driving shaft 4 so as to allow said rotary driving plate 14 and wobble slanting plate 12 to be inclined. The driving shaft 4 has a protrusion 22 extending through a longitudinal direction slot 20 of the sleeve 18, and provided with a guide slot 21 for guiding the inclination of the rotary driving plate 14. This protrusion 22 engages a lug 23 integrally formed with the rotary driving plate 14, and retained with respect to said lug 23 by a lateral pin 24 slidably guided within the guide slot 21. Although the wobble slanting plate 12 may be inclined together with the rotary driving plate 14, it is prevented from being rotated integrally with the rotary driving plate 14 by a guide pin 27 slidably mounted with a ball guide 26 which is held through a guide shoe 25 of a semi-circular cylindrical shape slidably mounted on the wobble slanting plate 12. A valve plate 28 provided with a suction port 29 and an exhaust port 30 has a suction valve disc 31 and a discharge valve disc 32 at its opposite sides, and is fixed between the cylinder block 1 and the rear case 2. There are also provided a discharge valve presser plate 33, a suction chamber 34, a discharge chamber 35, a crank chamber 36, a cylinder chamber 37 for the piston 10 at the side of the valve plate 28, a return spring 38 mounted on the driving shaft 4, and a control valve 39 provided in the rear case 2 for controlling the internal pressure in the crank chamber 36.
Functioning of the conventional wobble slanting plate is described hereinafter.
Upon driving of the driving shaft 4 from outside, the rotary driving plate 14 engaged with the protrusion 22 is rotated at an inclination angle, and based on the wobble motion of the non-rotating wobble slanting plate 12 through the thrust roller bearing 15, the pistons 10 each connected to the wobble slanting plate 12 by the rods 11 through the free-directivity ball joints 13, effect the reciprocating movement within the cylinders 9 in the axial direction, whereby the cooling medium gas flows into the cylinder chamber 37 through the suction port 29 in a suction stroke in which the piston 10 is displaced from an upper dead center to a lower dead center, and flows out from the cylinder chamber 37 through the exhaust port 30 in the compression and discharge strokes in which said piston 10 is displaced from the lower dead center to the upper dead center.
It is to be noted here that the performance control is intended to alter the volume of the cylinder chamber 37, i.e. displacement or exhaust amount thereof non-stepwisely by varying the stroke of the piston 10 through variation of the inclination angle of the wobble slanting plate 12. The inclination angle of the wobble slanting valve 39 for controlling the internal pressure of the crank chamber 36 at the back of the piston 10 with respect to the suction pressure, and balancing of force at the piston in which an exerting force based on the centrifugal force of the rotary driving plate 14 is produced on the piston 10. Accordingly, when a thermal load is high, the displacement i.e. exhaust amount is made maximum by rendering the inclination angle of the wobble slanting plate 12 largest through elimination of a pressure difference between the suction pressure and the internal pressure of the crank chamber 36. Meanwhile, when the thermal load is low, and the suction pressure becomes lower than that at the suction pressure control point set on the control valve 39, the control valve functions to raise the internal pressure in the crank chamber 36 and to reduce the inclination angle of the wobble swashing plate 12, and consequently, the stroke for the piston 10 is reduced for the reduction of the displacement or exhaust amount.
It should also be noted that the positions of the slanting plate 12 and the rotary driving plate 14 are determined by the pair of pivotal axis pins 19 connected to the sleeve 18, and the lateral pin 24 sliding within the guide slot 21 formed in the protrusion 22 of the driving shaft 4, thereby giving a constant upper dead center position to the piston 10.
The performance control of the wobble slanting plate type compressor as described above is of the system for varying the physical displacement in principle, and shows a comparatively superior performance control efficiency (At the period of 50% performance, the result coefficient ratio is about 90% with respect to the period of 100% performance).
However, the conventional wobble slanting plate type compressor has various problems as described hereinafter.
Firstly, the compression principle of the compressor which forms the basis of the arrangement is of the reciprocating system anyhow, which is low in volumetric efficiency (i.e. substantially effective discharge amount with respect to the displacement or exhaust amount). The main cause of such disadvantages is attributable to the compressed residual cooling medium gas volume at the upper portion of the piston and the resistance of the suction valve. This defect is one of the bottlenecks for the reduction in size and weight of a compressor.
Secondly, with respect to the internal pressure control for the crankcase in the control of the inclination angle for the wobble slanting plate, fine pressure control (0.3-0.5 kg/cm.sup.2) is required as well as the pressure control for a large space over one liter, thus presenting conditions disadvantageous to achieving sufficient response characteristics and control stability.
Thirdly, the fundamental construction of the compressor is of a system which has a large unbalanced physical load resulting from the wobble motion of the wobble swashing plate, and which is also inferior to the rotary type compressor in the noises arising from presence of the suction valve. Although the above disadvantages may be clearly alleviated during the performance control period as compared with compressors without such performance control function, vibrations and noises are still large under the operating conditions in which 100% performance is to be continued to the last.
Fourthly, with respect to the constructions related to the performance control function, due to presence of many sliding portions, there are some problems in the reliability and durability of members as well as in the lubricating characteristic.
In addition to the disadvantages as referred to above, there are many more problems to be solved such as matching characteristics to motor vehicles, costwise factors arising from the large number of parts, etc.
On the other hand, in a movable slanting plate compressor of the cylinder block rotating type having no suction valve, and disclosed, for example, in Japanese Patent Laid-Open Publication Tokkaisho No. 62-147055, there is a problem in the sealing between the cylinder block and the valve plate, with a large reduction of the volumetric efficiency during low speed rotation. Moreover, the conventional compressor referred to above is very complicated in the driving system for pistons, rods and holder plate, and also in the positioning mechanism, thus not being suitable for actual applications.